Valve and system for dental apparatus

ABSTRACT

A valve of the spool type, and a fluid flow system controlled by one or more of the valves. The valve is intended primarily for use with dental equipment and includes a spool having intersecting radial and axial passages, with a conical throttle member within the axial passage for controlling the rate of fluid flow into the axial passage from the radial passage. The valve body includes by-passes through the bore in which the spool is seated so that several of the valves may be arranged in banks without the need for separate manifolding.

ilmted States Patet 1 [111 3,757,423 Kraft Sept. 11, 1973 [54] VALVE ANDSYSTEM FOR DENTAL 3,556,669 1/1971 Valeska et al7 32/28 APPARATUS3,216,442 1/1965 Roth et al 137/209 3,414,000 12/1968 Newton 137/209[76] Inventor: Donald E. Kraft, 923 Winona Blvd,

Rochester 14617 Primary ExaminerRobert Peshock [22] Filed: May 6, 1970Att0rneyH0ffman Stone 21 Appl. No.: 35,005

Related US. Application Data [63] Continuation-in-part of Ser. No.367,294, May 14,

1964, Pat. No. 3,533,445.

[52] US. Cl. 32/22, 137/209 [51] Int. Cl. A61c 19/02 [58] Field ofSearch 137/209, 587; 32/22 {56] References Cited UNITED STATES PATENTS3,346,957 10/1967 Maurer et al. 32/22 3,445,934 5/1969 Harris 32/22 1WORK/N6 FL 0/0 I 57] ABSTRACT A valve of the spool type, and a fluidflow system controlled by one or more of the valves. The valve isintended primarily for use with dental equipment and includes a spoolhaving intersecting radial and axial passages, with a conical throttlemember within the axial passage for controlling the rate of fluid flowinto the axial passage from the radial passage. The valve body includesby-passes through the bore in which the spool is seated so that severalof the valves may be arranged in banks without the need for separatemanifolding.

4 Claims, 8 Drawing Figures PATENTEU SE?! 1 I973 SHEET 1 0F 3 F/ 6 (/AEWORK/N6 INVENTOR. DONALD E. KRAFT ATTORNEY PATENTED 1 3.757. 421

SHEEI 2 0F 3 a 12 1/6 06 a i HHIIH m /Z8 //l //0 80 F/GUAEJ fiVGZ/AfINVENTOR.

DONALD E. KRAFT t ATTORNEY VALVE AND SYSTEM FOR DENTAL APPARATUS BRIEFSUMMARY This application is a division of my co-pending application,Ser. No. 367,294, filed May 14, 1964, and now US. Pat. No. 3,533,445issued on Nov. 3, 1970.

This invention relates to novel dental apparatus and to a novel valve ofthe spool type particularly suited for use in the apparatus.

Modern dental equipment, particularly of the type wherein the workingtools are driven by air turbines, presents a relatively difficultvalving problem. As many as four different fluids must be supplied tothe dental hand piece during operation. l-leretofore, control of thevarious fluids has been accomplished by 'an array of separate, solenoidoperated valves, and, especially where the dentist's pedestal isequipped with two, three, or four different hand pieces, the plumbingarrangements have been complex and bulky, and difficult to assemble andto service.

Accordingly, one important object of the invention is to provide a valvecapable of simultaneously controlling any desired number of fluids inseparate circuits, the valve including separate, externally adjustablethrottle means for as many of the fluids as desired.

Other objects are: to provide a valve of this type including built-inmanifolding connections, whereby any desired number of the valves may beconnected to common sources of fluid supply without the need forexternal manifolding; to provide a valve of this type including O-ringseals between relatively movable parts therein, the parts being soarranged that the O-rings do not move over radially facing ports.

The invention also includes a novel liquid supply arrangement, wherebythe supply liquids are contained in closed systems, and their flow iscontrolled by alternately pressurizing and venting the systems, therebyavoiding the need to provide separate flow control valves in each liquidline. I

DETAILED DESCRIPTION The foregoing and other objects and advantages oftheinvention will become apparent from the following detaileddescription of representative embodiments thereof, taken in conjunctionwith the drawings, wherein: p r

FIG. 1 is a partly schematic diagram of a dental system according to thepresent invention including four hand pieces of the air turbine type andfour spool valves of the invention;

FIG. 2 is a plan view of the array of the four valves of the inventionas arranged in FIG. 1;

FIG. 3 is a longitudinal sectional view on an enlarged scale taken alongthe line 3-3 of FIG. 2 showing one of the spool valves in its closedposition, portions of the section being broken away in order to show allthree of the controlled fluid circuits;

FIG. 4 is a fragmentary longitudinal sectional view taken along the line4-4 of FIG. 2;

FIG. 5 is a side elevational view, partly in section of a spool valveaccording to a modified form of the invention, the valve beingoperatable manually instead of pneumatically, and showing the valve inits open position;

FIG. 6 is a cross-sectional viewtaken along the line 6-6 of FIG. 5;

FIG. 7 is a fragmentary, longitudinal sectional view of a hose couplingdevice according to the invention, attached to the discharge end of thespool valve; and

FIG. 8 is a side elevational view, partly in section showing a hosecoupling device according to the invention for attachment to one of thedental hand pieces.

Briefly, the invention contemplates a spool valve including a bodyhaving a step-tapered bore and radial inlet ports in the bore. Astep-tapered spool fits slidably within the bore and includes separate,axially extending ducts, one for each fluid to be controlled by thevalve. Radial ducts provide communication between the respective axialducts and the outer surface of the spool. Externally accessible needlevalves are fitted in the respective axial ducts for controlling the rateof fluid flow through them. The outlets of the valve to the utilizationdevices are axially through one end of the, spool, or on a portion ofthe spool surface that extends out of the bore. Additional, non-valvedoutlets are provided in the body for manifolding purposes so that eachsupply fluid may flow substantially unimpeded through the valve. Aplurality of the valves may thus be arranged in an array with theircorresponding fluid circuits in parallel with respect to the fluidsources.

The valve makes use of O-rings for sealing between the spool and thebody. The bore of the valve body is step-tapered so that the O-rings,which in the illustrated embodiments are carried in grooves on thespool, do not pass over the radially facing ports in the bore, butinstead engage only smooth, unbroken cylindrical wall portions of thebore and axially facing annular shoulders therein. Because of the doublecurvature of the ports it is extremely difficult to smooth their edgesso that they will not unduly abrade an O-ring rubbing over them. On theother hand, it is a relatively simple matter to provide a smooth finishon an axially facing shoulder. In the practice of the invention, contactby the 0- rings against the radially facing ports is avoided by therelatively simple expedient of tapering the bore. The bore is readilymachinable by simple drilling and breaching methods. No radially facinggrooves are required in it, a feature that materially reduces its costrelative to other spool valves which require grooves to be milled withinthe bore of ,the body.

Another feature of the invention pertains to the control of the supplyliquids. Only the air supply is valved. The liquids are contained inseparate, closed systems, which are alternately pressurized and ventedaccording to demand, thus reducing the number of valves in the over-allsystem.

Referring now to the drawings, FIG. 1 is a schematic diagram of a dentalequipment system including four hand pieces 10, ll, 12, and 13,respectively, and four selector spool valves l6, 17, 18, and 19,respectively, of the invention, each one of the spool valves beingassociated with a different respective one of the hand pieces. Thevalves 16-19 are actuated by a pressure fluid such as compressed air inresponse to actuation of solenoid valves '22, 23, 24, and 25,respectively, which are connected between the source (not separatelydesignated) of the pressure fluid and the respective valves 16-19. Thesolenoid valves 22-25, in turn, are actuated in response to the closingof separate, normally closed limit switches 28, 29, 30, and 31,respectively, which are individually held open by the respective handpieces 10-13 when the hand pieces are in their receptacles on thepedestal (not shown). When the dentist selects a particular hand pieceand removes it from its receptacle, the corresponding limit switch 28,29, 30, or 31 closes, the corresponding solenoid valve 22, 23, 24, or 25is actuated to admit pressure fluid to the actuating cylinder 134 of thecorresponding selector valve 16, 17, 18 or 19, and the selector valve isthereby actuated to its open position.

The controlled fluids in the system as illustrated are five in number:

First, pressure air for air bearings in the turbines of the first twohand pieces 10 and 11 is delivered directly from the source to the firstselector valve 16 through a conduit 34, and, through the body of thevalve 16 and a nipple 36, to the second valve 17. This air supply is notvalved responsively to operation of the dentists foot pedal 38, but isalways available in the two valve bodies 16 and 17, because it isdesired to maintain the flow of air for hearing purposes at all timeswhen either hand piece 10 or 11 is out of its holder in order to keepthe bearing operative while the turbine is decelerating.

Second, air for driving the turbines in the hand pieces 10-13 isdelivered to all of the valves 16-19 through a conduit 40, the air beingby-passed around the valve spools in each of the first three valves 16,17, and 18, and passing through the nipples 42, 43, and 44.

Third, a first liquid, which may be, for example, plain water, isdelivered to the first three spool valves 16, 17, and 18 from a firstpressure container 46 through a conduit 48, the liquid passing throughthe body of the first valve 16 and the connector nipple 50 to the secondvalve 17, and through the body of the second valve and a connectornipple S1 to the third valve 18.

Fourth, a second liquid, which may be, for example, lubricating oil forthe oil bearings in the turbines of the second two hand pieces 12 and13, is delivered to the second two spool valves 18 and 19 through aconduit 54 from a second pressure vessel 52, the liquid passing throughthe body of the last spool valve 19 and a connector nipple 56 to thethird valve 18.

Fifth, a third liquid, which may, for example, be a solutionof adetergent in water, is delivered from a third pressure vessel 58 througha conduit 60 to the last spool valve 19 only.

As will be described in greater detail hereinafter in connection withthe description of the internal struc ture of the spool valves 16-19,the controlled fluids are free to pass in a horizontal direction throughthe body of each valve substantially without obstruction. Closureelements as indicated by the crosses 62 and 63 are provided between therespective valves when it is desired to seal off their correspondinginlet ports one from the other. The controlled outlets of the spoolvalves 16-19 lead into individual multi-passage hoses 64, 65, 66, and67, respectively, which lead from the respective valves 16-19 to therespective hand pieces 10-13.

The pressure tanks 46, S2, and 58 are connected to the pressure fluidsource through a three-way solenoid valve 68, which alternately connectsthe pressure tanks 46, 52, and 58 to the pressure fluid and to theatmosphere in response to the opening and closing of the pedal-operatedswitch 70. The pressure air for driving the turbines in the hand pieces10-13 enters the conduit 40 after passing through the three-way valve 68and the pedal-actuated throttle valve 72.

in operation, after removing one of the hand pieces 10-13, there isusually an interim waiting period during which the dentist prepares touse the hand piece. During this period, before the dentist depresses hisfoot pedal control 38, the three-way solenoid valve 68 remains closed,and working air is delivered only to the conduit 34 for maintaining theair bearings and to the actuating cylinder of the valve associated withthe selected hand piece. None of the liquids flow, because all of thepressure tanks 46, 52, and 58 are vented to atmosphere through the valve68.

When the dentist actuates the control pedal 38, the switch 71 closes toactuate the 3-way solenoid valve 68, which thereupon admits pressure airto the throttle valve 72 and to the three pressure tanks 46, 52, and 58.Air for driving the turbine in the hand piece flows through the throttlevalve '72, the conduit 18 and the open one of the spool valves 16-19 tothe hand piece 10-13.

When he is through using the hand piece, the dentist releases the pedal38, thereby opening the switch and de-actuating the 3-way solenoid valve68, which thereupon vents the pressure tanks 46, 52, and 58 toatmosphere to stop the liquid flow, and also closes off the turbinedrive air supply. When the dentist returns the hand piece to its holder,the hand piece limit switch 28, 29, 30 or 31 opens to de-actuate theactuator solenoid valve 22, 23, 24, or 25, and thereby to tie-actuatethe corresponding spool valve 16, 17, 18, or 19.

The assembly of spool valves 16-19 is secured together in the embodimentshown by two tie bars 74, which pass through horizontal holes in thebodies of the respective valves, and maintain sealing pressure betweenthe valve bodies and the respective nipples and stoppers 36, 42, 43, M,50, S1, 56, and 62, and between the connector end plates 76 and 78 andthe first and last valves 16 and 19, respectively. If desired, however,the assembly may be secured by soldered fittings between the variousparts or by any other desired means.

FIG. 3 shows a cross-section of the first one 16 of the valves, all ofthe valves 16-19 being identical, except that the end ones 16 and 19 areprovided with connector plates 76 and 78, while the intermediate onesare fitted with the connector nipples. The valve 16 includes a body 80of square cross-section mid having a step tapered bore 82. The bore 82is divided into four sections 84, 85, 86, and 87 by three annular,inclined shoulders 90, 91, and 92, respectively. The sections 84, 85,86, and 87 of the bore are of successively smaller diameters. Twodiametrically opposed ports 94 and 95, re spectively, extend through thebody wall and open into the uppermost and largest section 84 of thebore. Similarly, two ports 96 and 97 extend through the body wall andopen into the second section of the bore. And lastly, a third pair ofdiametrally opposed ports 98 and 99 extend through the wall of the body811 and open into the third section 86 of the bore.

A spool 1041, shown in its closed position in FIG. 3, fits slidablywithin the bore 82 of the body. The spool 100 does not close off orsubstantially affect communication between any pair of the ports 94-99that open into a common section of the bore 82. For example, a fluidentering into the valve body through the port 94 is free to circulatearound the spool 111i) and exit through the port regardless of theposition of the spool at any given moment.

Resilient, compressible O-rings 102, 1113, 16m, 165, 106, 107, and 188,carried by the spool res and fitted in grooves (not separateiydesignated) therein, engage the walls of the bore 82 and constitute thevalve seals. The use of O-rings allows greater tolerances in manufactureas compared to spool valves having metal lands. At the top of the spool100, the first O-ring 102 seals against the wall of the top portionsection 84 of the bore for all positions of the valve, and is alwaysabove the two ports 94 and 95 which open into the top section 84. TheO-ring 102 rubs and rolls only against the smooth, unbroken part of thebore section 89. Similarly, the third O-ring 104, the fifth O-ring 106,and the seventh O-ring 108 always remain in sealing engagement with thesmooth, unbroken parts of, respectively, the second section 85, thethird section 86, and the fourth section 87 of the bore. The secondO-ring 103, the fourth O-ring 105, and the sixth O-ring 107 ride, duringmotion of the valve, over the respective annular shoulders 90, 91, and92, which separate the different bore sections. When the spool 100 movesupwardly to its full open position, these O-rings 103, 105, and 107 moveinto the respective next larger sections 81, 85, and 86 of the bore, andstand clear of the bore as shown for the second O-ring 103 in FIG. 5.

The spool 100 as shown has three separate axial passageways 110, 111,and 112, extending the entire length of the spool and opening at bothends thereof, and three axially spaced radial passageways 114, 115, and116, which respectively intersect the three axial passageways 110, 111,and 112. The first radial passageway 1 14 opens exteriorly of the spoolin an annular groove 118 about midway along the length of the spoolbetween the fourth and fifth O-rings 105 and 106. The second radialpassageway 115 opens exteriorly of the spool within an annular groove119 between the second and third O-rings 103 and 104. Similarly, thethird radial passageway 116 opens in an annular groove 120 locatedbetween the last two O-rings 107 and 108. Portions (not separatelydesignated) of the axial passageways are threaded to receive adjustableneedle valves 122, 123, and 124, respectively, the needle portions ofwhich extend adjustably across the radial passageways. When the needlevalves 122, 123, and 124 are driven downwardly, they close communicationbetween the radial passageways 1.14, 115, and 116 and. the lower partsof the respective axial passageways 110, 111, and 112.

The spool 100 extends beyond the lower end of the body 80, and anannular adapter 128 is fixed to the lower end of the spool 100. Theadapter 128 includes an outwardly extending flange 130, and acompression coil spring 132 is fitted between a flange 134 at the bottomof the body and the flange 130 of the adapter for biasing the spooltoward its downward limit position in the body 80, and for returning thespool to its closed position when the valve is de-actuated.

The valve is actuated to its open position by pressure air, which entersthrough an inlet fitting 130 (FIG. 4) angularly spaced from the regularports 94-99 of the body. The air then passes through an axial passageway132 in the body 80, and upwardly into a cup-shaped member 134 which isfixed and sealed to the body 80 at the upper end thereof. The pressureair then raises the piston 136, which is slidable within the member 134,and which is secured to the upper end of the spool 100. The upwardtravel of the spool 100 in the body 80 is limited by the abutment of theadapter 128 against the lower end of the body 80. The annular groove 138on the bottom face of the piston is provided in order to insuredistribution of the pressure air fully around the piston at thebeginning of the actuating stroke.

When the spool is actuated to its upper, or open position, as shown inthe manually actuated embodiment illustrated in FIG. 5, the grooves 118,119, and 120 are brought into the respective bore sections immediatelyabove the sections where they lie in the closed position, thuspermitting the respective fluids to pass into the radial passageways 114, 1 15, and 1 16, through the needle valves and the respective axialpassageways and out the lower end of the spool. When the spool is in itsclosed position, as seen in FIG. 3, the grooves 118, 119, and 120 aresealed off by their respective pairs of O-rings from communication withthe ports 94-99.

As illustrated in FIG. 5, a quick-acting left-and-right hand threadarrangement 1 .10 may be used for raising and lowering the spool in thevalve body by manual actuation of a knurled nut 142, in place of thepneumatic actuator hereinabove described.

The manually operatable valve 16 illustrated in FIG. 5 is more compactthan the fluid actuatable valves 16-19 in that the actuating screwmechanism 140 is of smaller diameter than the width of the valve bodyand does not extend radially outwardly beyond the side walls of the bodyas do the actuating cylinders 134 of the fluid actuatable valves 16-19.Connecting nipples, therefore, are not required for connecting themanually actuatable valves in parallel flow arrangement. The manualvalves 16' may be so connected merely by securing them directly togetheras shown in FIG. 5.

When it is desired to block off one of the fluid circuits between anytwo valves of an array, flow blocking means such as the disc 143(FIG.'3) may be placed within the O-ring in the port at the outersurface of the valve body 80 at the desired point in the circuit. Bythis means, each of the fluid circuits in an array of the valves may bedivided into two parts, one part receiving one fluid from one end of thearray, and the other part receiving a different fluid from the oppositeend.

In the manually actuatable'valve 16' shown in FIG.

5, it is necessary to key the spool against rotationrelative to the body80' in order to hold the spool against rotation during operation of thescrew type at:- tuating device 140. It is also preferred to key thespool 100 of the pneumatically actuatable version against rotationrelative to its body 80 in order to maintain the angular alignment ofthe needle valves relative to the body 80.

As shown in FIGS. 3, 5, and 6, the spools 100 and 100' are keyed totheir respective bodies 80 and 80 by an internally threaded hexagonalsleeve 145, which is threaded onto the lower end of the spool 100 or 100and locked thereon by the adapter or 128'. The sleeve 145 fits slidablywithin an hexagonal aperture 147 in a disc 149, which is fixed to thebottom of the body 00 or 00. 1

FIG. 7 illustrates a connector according to the invention for effectinga connection between the multiinwardly extending annular flange 148therein. The disc 146 carries a first tube 150, which fits within thelargest passageway 110 in the valve spool, and separate reversely benttubes 162 (only one of which is shown) which fit loosely into thesmaller outlet passages 111 and l 12, respectively, and extenddownwardly from the disc. The tubes 15% and 162 are sealed, as, forexample, by soldering to the disc 146. The disc 146 also includes anannular flange 152, which extends downwardly beyond the lower end of thenut 144, and which is externally threaded to receive a clamping nut 154.

An annular insert 156 rests in endwise abutment against the bottomsurface of the disc 146, and within the flange 152. The lower endportion 158 of the insert is downwardly tapered to fit into and slightlydilate the hose 64.

The inner surface 163 of the lower end of the clamping nut is alsotapered at about the same angle as the taper of the insert 156. The hose64 is thus firmly clamped between the insert 15 and the nut 154. The useof the insert 15d enables the use of a hose 64 of a smaller diameterthan would be required to match the diameter of the outlet end of thespool 100. It also enables the provision of a relatively large spacewithin the flange 152 of the disc to facilitate attachment of theconnector to the spool.

Before the clamping nut 154 is threaded upon the flange 152, thereversely bent tubes 162 are inserted into the small diameter innertubes 166 in the hose.

A flat gasket 168 provides a seal between the outlet end of the spool100 and the upper surface of the disc 146.

it has heretofore been the general practice to feed a mist oflubricating oil into the turbine drive air stream at a point close tothe end of the conduit where the turbine drive air enters it. This hasled to certain difficulties, primarily due to the tendency of the oil tocondense in the air line, and, as a result, to flow irregularly into thehand piece, at times flooding the turbine.

This difficulty is overcome in the practice of the present invention bythe provision of a separate passageway 168 for the lubricating oil,leading from the valve, to the hand piece, and terminating at the handpiece in a vaporizing nozzle H70 as shown in FIG. 8. The venturi effectof the turbine drive air passing by the nozzle assists in dispersing theoil into a fine mist just as it enters the hand piece, a point closeenough to the turbine that the oil does not condense before reaching it.The turbine always has a steady supply of lubricating oil at the properrate.

What is claimed is:

l. A fluid flow control system comprising:

a. an air drivable tool,

b. a pressure vessel for containing a liquid, said vessel having inletand outlet ports,

c. conduit means connecting said outlet port to a discharge orificeadjacent to said tool,

d. a master three-way valve for selectively connecting said tool to asource of compressed air, and venting said tool to atmosphere, and

e. conduit means connecting said pressure vessel to the outlet of saidthree-way valve in parallel with said tool, whereby the vessel ispressurized when and only when the source of compressed air is connectedto the tool.

2. A fluid flow control system for use in dental equipment of the typeincluding a plurality of hand pieces each having an air driven turbine,the hand pieces being arranged for selective alternate use, each one ofsaid hand pieces requiring the simultaneous supply of a plurality offluids during operation, one of the fluids being a liquid, and anotherone of the fluids being air for driving the turbine, the equipmentincluding a valve for controlling the flow of the turbine driving air,said system comprising:

a. a plurality of selector valves, one for each of the hand pieces,

b. means connecting the outlets of said selector valves to respectiveones of the hand pieces,

c. means for selectively actuating said selector valves,

d. a pressure vessel for holding the liquid, said vessel having anoutlet port and an inlet port,

e. conduit means connecting said outlet port of said vessel to saidselector valves,

f. a three-way valve for connection between a source of pressure gas andsaid inlet port of said vessel, and

g. means responsive to actuation of the valve that controls the flow ofthe turbine drive air for actuating said three-way valve, said three-wayvalve being arranged to connect said inlet port to the source ofpressure gas whenever the turbine air valve is open and to vent saidinlet port to the atmosphere at all times when the turbine air valve isclosed.

3. A fluid flow control system according to claim 2 including means forinjecting a lubricant into the air for driving the turbine of each ofsaid hand pieces during times when the turbines are operating, saidinjecting means being arranged to inject the lubricant at points closeto the air inlet ports of the respective hand pieces.

4. A fluid flow control system according to claim 2 including areservoir for a lubricant, and conduit means connecting said reservoirthrough said selector valves to the working air inlet ports of each ofsaid hand pieces, whereby when said hand pieces are operating, lubricantis injected into the working air at points close to the turbines andcondensation of the lubricant out of the working air is minimized.

1. A fluid flow control system comprising: a. an air drivable tool, b. a pressure vessel for containing a liquid, said vessel having inlet and outlet ports, c. conduit means connecting said outlet port to a discharge orifice adjacent to said tool, d. a master three-way valve for selectively connecting said tool to a source of compressed air, and venting said tool to atmosphere, and e. conduit means connecting said pressure vessel to the outlet of said three-way valve in parallel with said tool, whereby the vessel is pressurized when and only when the source of compressed air is connected to the tool.
 2. A fluid flow control system for use in dental equipment of the type including a plurality of hand pieces each having an air driven turbine, the hand pieces being arranged for selective alternate use, each one of said hand pieces requiring the simultaneous supply of a plurality of fluids during operation, one of the fluids being a liquid, and another one of the fluids being air for driving the turbine, the equipment including a valve for controlling the flow of the turbine driving air, said system comprising: a. a plurality of selector valves, one for each of the hand pieces, b. means connecting the outlets of said selector valves to respective ones of the hand pieces, c. means for selectively actuating said selector valves, d. a pressure vessel for holding the liquid, said vessel having an outlet port and an inlet port, e. conduit means connecting said outlet port of said vessel to said selector valves, f. a three-way valve for connection between a source of pressure gas and said inlet port of said vessel, and g. means responsive to actuation of the valve that controls the flow of the turbine drive air for actuating said three-way valve, said three-way valve being arranged to connect said inlet port to the source of pressure gas whenever the turbine air valve is open and to vent said inlet port to the atmosphere at all times when the turbine air valve is closed.
 3. A fluid flow control system according to claim 2 including means for injecting a lubricant into the air for driving the turbine of each of said hand pieces during times when the turbines are operating, said injecting means being arranged to inject the lubricant at points close to the air inlet ports of the respective hand pieces.
 4. A fluid flow control system according to claim 2 including a reservoir for a lubricant, and conduit means connecting said reservoir through said selector valves to the working air inlet ports of each of said hand pieces, whereby when said hand pieces are operating, lubricant is injected into the working air at points close to the turbines and condensation of the lubricant out of the working air is minimized. 